While some of the tens of thousands of foreign troops based in Afghanistan are fighting against the Taleban, others are involved in rebuilding and developing the country's infrastructure. But a debate is starting to emerge about whether the current strategy of reconstruction is becoming a hindrance.

The Salang Tunnel connects north and south Afghanistan

On the road north from Kabul towards the Salang tunnel, in the town of Parwan, they are selling grapes and melons from the roadside stalls.

Not far from the road, shimmering in the late afternoon sun , a line of new electricity pylons stretches into the distance.

Soon - not soon enough say residents of the capital - they will provide round-the-clock power to Kabul, all the way from Tajikistan.

Building bridges

The area around Parwan has seen its fair share of military campaigns over the years.

Genghis Khan fought here in 1221. The Bengal Cavalry was defeated in 1840 and more recently, in the late 1990s, there was heavy fighting between the Taleban and the mujahideen.

These days a different type of campaign is in full swing - reconstruction.

Foreign troops and aid agencies are both providing aid in Afghanistan

On the outskirts of town, a bridge is being built by a local company. Not a particularly big one, but important for the residents who live there.

Along with a series of channels and retaining walls, it will prevent water flooding through their homes when winter snows melt in the nearby mountains.

The money to build the bridge - and plenty of other projects around Parwan - has come from the local PRT.

Three letter acronyms - TLAs to you and me - are all the rage in Kabul. A PRT is a Provincial Reconstruction Team - a combination of soldiers and civilian experts - run by the military. In charge around Parwan are American soldiers from the nearby Bagram air base.

Some aid agencies also complain that the line between military and humanitarian assistance has become dangerously blurred

What happens is this. Local people decide what kind of project they want, schools, irrigation schemes, or perhaps a new mosque. They go to the local governor and the governor goes to the PRT to get money and help. And across the country, that runs to billions of dollars.

The theory is simple. Foreign military forces help reconstruct Afghanistan at the same time that they fight the Taleban.

But there are several problems. The presence of PRTs, and the money they control, means local government in Afghanistan is not developing as well as it might.

Some aid agencies also complain that the line between military and humanitarian assistance has been blurred, making their work more difficult and more dangerous.

In fact, internal UN documents reveal that the security situation for aid workers has deteriorated dramatically.

Nearly all areas of southern and eastern Afghanistan are now described as extreme or high risk. That was not the case a couple of years ago.

Parts of the north and west, once considered quite safe, have become less secure. There are now districts close to Kabul where UN teams are no longer allowed to work.

In that sense, things are not going to plan.

'Exit strategy'

So should the whole concept of PRTs be thought through again? Should more effort be made to place decisions, and money, in Afghan hands?

There are 25 PRTs across the country, about half of them run by the Americans, the rest by troops from 12 other nations.

Some of them - such as the British in Helmand or the Dutch in Uruzgan - really could not function without a robust military presence.

In the end, most Afghans want local solutions to their problems

But a recent report from the World Bank is surprisingly blunt in its analysis.

"In trying to create the space for the Afghan state to develop," it argues, "PRTs run the risk of undermining it. They should really only exist," it concludes, "where security conditions make them absolutely necessary."

That is hardly the case in somewhere like Parwan.

But talk of closing PRTs is extremely sensitive. Senior Nato officials fear any discussion of an exit strategy would be used by some countries as an excuse to pack up and leave straight away.

Reconstruction debate

In the end, most Afghans want local solutions to their problems. But with corruption still endemic, they wonder how to get from here to there.

One of the engineers by the half-built bridge in Parwan is emphatic.

PRTs have done an enormous amount of good. But are they the right long-term solution?

"We need a president with a big stick,' he says. "But one honest man can do nothing if he's surrounded by crooks."

His companion nods and points to the remains of a nearby guard-post.

The mud-brick walls are crumbling and a slab of corrugated iron is balanced precariously on what is left of the roof.

"This," he says, "is the condition of Afghanistan right now."

No-one would deny that it needs rebuilding. But debate is intensifying about whether the international community is doing that in the best way.

PRTs have done an enormous amount of good. But are they the right long-term solution? Some people do not really want to talk about it. Changing tack is seen as defeatist.

This is a debate, though, which will have a profound impact on the future of this battered country, and on the involvement of foreign troops who are fighting and dying there.